Starters that are used for starting internal combustion engines require currents up to 3000 A. Said currents are switched via an electromagnetic switch.
The magnetic armature, as claimed in the prior art, is drawn in by a magnetic field which is generated in the magnetic field windings and presses the switching axis with the contact bridge onto the contacts in the switch cover. This closes the connection between the battery and the electric motor of the starter. In the case of corresponding demands, the relay can be protected against ingress of water and other media from the surrounding area by means of a protective cap produced from an elastomer. Where a rapid increase in the temperature of the relay is caused by the motor, e.g. by traveling at high load (tow load or speed load) or by a rapid drop in atmospheric pressure caused by traveling uphill, the air in the relay expands, the protective cap swells and the relay is possibly no longer able to switch. This means that the functioning of the starter is no longer certain.
It is known from the prior art to admit a hole several millimeters large into the protective cap in order to ensure pressure compensation. However, media such as water or dirt are also able to penetrate into or emerge from the relay via said hole.
Between the core and the switch cover there is usually another cup spring. A seal is obtained in a circumferential manner in the region between the protective cap and the fixed magnetic core by the bead of the protective cap being pressed onto the relay housing by means of a retaining ring (not shown in the drawing).